An example snippet of how to add a 3D annotation into an AR scene.

snippet.swift

func showResult(_ result: String) {
    // HIT TEST : REAL WORLD
    // Get Screen Centre
    let screenCentre : CGPoint = CGPoint(x: self.sceneView.bounds.midX, y: self.sceneView.bounds.midY)

    let arHitTestResults : [ARHitTestResult] = sceneView.hitTest(screenCentre, types: [.featurePoint]) // Alternatively, we could use '.existingPlaneUsingExtent' for more grounded hit-test-points.

    if let closestResult = arHitTestResults.first {
        // Get Coordinates of HitTest
        let transform : matrix_float4x4 = closestResult.worldTransform
        let worldCoord : SCNVector3 = SCNVector3Make(transform.columns.3.x, transform.columns.3.y, transform.columns.3.z)

        // Create 3D Text
        let node : SCNNode = createNewResultsNode(result)
        resultsRootNode.addChildNode(node)
        node.position = worldCoord
    }
}

func createNewResultsNode(_ text : String) -> SCNNode {
    // Warning: Programmatically generating 3D Text is susceptible to crashing. To reduce chances of crashing; reduce number of polygons, letters, smoothness, etc.
    print("shwo result: \(text)")
    // Billboard contraint to force text to always face the user
    let billboardConstraint = SCNBillboardConstraint()
    billboardConstraint.freeAxes = SCNBillboardAxis.Y

    // SCN Text
    let scnText = SCNText(string: text, extrusionDepth: CGFloat(textDepth))
    var font = UIFont(name: "Helvetica", size: 0.15)
    font = font?.withTraits(traits: .traitBold)
    scnText.font = font
    scnText.alignmentMode = CATextLayerAlignmentMode.center.rawValue
    scnText.firstMaterial?.diffuse.contents = UIColor.orange
    scnText.firstMaterial?.specular.contents = UIColor.white
    scnText.firstMaterial?.isDoubleSided = true
    scnText.chamferRadius = CGFloat(textDepth)

    // Text Node
    let (minBound, maxBound) = scnText.boundingBox
    let textNode = SCNNode(geometry: scnText)
    // Centre Node - to Centre-Bottom point
    textNode.pivot = SCNMatrix4MakeTranslation( (maxBound.x - minBound.x)/2, minBound.y, textDepth/2)
    // Reduce default text size
    textNode.scale = SCNVector3Make(0.2, 0.2, 0.2)

    // Sphere Node
    let sphere = SCNSphere(radius: 0.005)
    sphere.firstMaterial?.diffuse.contents = UIColor.cyan
    let sphereNode = SCNNode(geometry: sphere)

    // Text Parent Node
    let textParentNode = SCNNode()
    textParentNode.addChildNode(textNode)
    textParentNode.addChildNode(sphereNode)
    textParentNode.constraints = [billboardConstraint]

    return textParentNode
}